Activity in 2014 and Science plan in FY2015

Ocean observation

Hakuho-maru cruise (May 2014) : Recovery of sediment trap at K2

Long-term change of Lithogenic Materials in the western subarctic gyre (increase of eolian dust?!)

Kaiyo cruise (June 2014): Start of KEO Time-Series observation

Increase of chl-a after pass of typhoon


Pre- and post-Fengsheng MODIS SST

Pre- and post-Fengsheng MODIS Chl

JAMSTEC KEO sediment trap

Shinsei-maru cruise (Oct. 2014): Recovery / Re-deployment of sediment trap at F1

Ongoing lateral transport of radiologically contaminated sediment
TEPCO Fukushima NPP1
(1.5km off FNPP1, Oct 2014 KS-14-20)


Publication 1: Sinking velocity of particulate radiocesium

Honda, M. C. and H. Kawakami: Sinking velocity of particulate radiocesium in the northwestern North Pacific, Geophysical Research Letters, 41, 3959–3965, doi:10.1002/2014GL060126. (2014)

Time-lag of peak of concentration and the final detection period between 500 m and 4810 m was about 80 days while that of the first detections was only about 16 days.
Decrease in SV with time
■Early and small fraction: refractory (“Cesium Ball”?!)
■Most of particulate 137CS: labile
(Sulfate ?!)

Publication 2: Light limitation of Primary Productivity in the western subarctic gyre

Matsumoto, K., M. C. Honda, K. Sasaoka, M. Wakita, H. Kawakami, and S. Watanabe: Seasonal variability of primary production and phytoplankton biomass in the western pacific subarctic gyre: Control by light availability within the mixed layer. Journal of Geophysical Research: Oceans 119, doi:10.1002/2014JC009982. (2014).

In the western Pacific subarctic gyre, phytoplankton increases in summer when insolation is high and surface mixed layer is shoaled. Nutrient is never deficient all year round and this area is categorized into High Nutrient Low Chlorophyll (HNLC) area.
Primary productivity (PP) correlated well with insolation (PAR). Even in summer, when PAR is lowered by “sea fog”, PP decreased. In the western Pacific subarctic gyre, limiting factor of phytoplankton biomass and PP is not only Fe but also light while Fe in the eastern Pacific subarctic gyre.

Publication 3: Factors controlling phytoplankton variation and seasonal bloom onset

Siswanto, E., K. Matsumoto, M. C. Honda, T. Fujiki, K. Sasaoka, and T. Saino. Reappraisal of meridopnal differences of factors controlling phytoplankton biomass and initial increase preceding seasonal bloom in the northwestern Pacific Ocean. Remote Sensing of Environment 159, 44-56 (2015)

Science plan in FY2015

1. Ocean observation

(1) NOAA-PMEL cruise (2015.8.27 ~ 9/12):

Recovery / Redeployment of KEO Sediment trap
□ Change in settling particles after typhoon?
□ Discussion about other triggers including meso-scale eddy and eolian dust

NOAA cruise M/V Blue Fin (50 m(L) x 11.5 m(w))

(2) Shinsei-maru cruise (KS-15-13: 2015/10/7~10/16)

Recovery / Redeployment of F1 Sediment trap
□ Investigation of Fukushima-derived radionuclides

(3) Eastern Indian Ocean cruise(MR15-05: 2015/12/23~2006/1/28)

□ Observation of basic environment regarding aerosol and ecosystem for future IIOE-2 related Bay of Bengal Cruise

2. Publication

□ JO K2S1 project special issue

3. Sample / Data analysis

□ Dissolution experiment of aerosol
□ Analysis of REE and mineral in sediment trap sample